(1) Field of the Invention
This invention relates to a solvent for the dye of pressure-sensitive recording paper. More particularly, the invention relates to the solvent for the dye of pressure-sensitive recording paper which solvent is prepared from a heavier product that is obtained in the ethyltoluene production process by alkylating toluene with ethylene in the presence of synthetic zeolite catalyst.
(2) Description of the Prior Art
Various kinds of pressure-sensitive recording papers are hitherto well known. For example, a colorless dye, that is a dye-precursor, is dissolved in a solvent and the obtained solution is encapsulated into microcapsules by conventional methods. One surface of a sheet of paper is applied with the microcapsules and the surface of another sheet of paper is applied with a color developer such as clay or polymeric material which produces a color upon reacting with the dye. When the recording paper is used, the treated surfaces of the above set of paper sheets are put together face to face and local pressure is applied to the paired sheets by handwriting or typewriting, thereby obtaining desired duplicate impressions. Besides the above, several kinds of pressure-sensitive recording papers similar to the above are also known. These pressure-sensitive recording papers are used for duplicating and registering.
The recording mechanism in the pressure-sensitive recording paper is such that the microcapsules on the surface of a sheet of paper are ruptured by the pressure of handwriting or by the impact of typewriting to release the dye solution from the microcapsules. The solution containing a dye comes into contact with the color developer on the opposing surface of the other sheet of paper to produce a color. There may be another type of pressure-sensitive recording paper such that on the same surface of the paper are coated the color developer and microcapsules containing therein a dye solution.
The dyes for the pressure-sensitive recording paper are exemplified by Crystal Violet Lactone, Malachite Green, benzoyl Leucomethylene Blue, Rhodamine B, and 3-dialkylamino-7-dialkylamino fluoran.
The solvents for dissolving the dyes (to be exact, dye-precursors) are required to have the properties as follows:
(a) to have no toxicity and no offensive odor,
(b) to be colorless or quite light-colored, and developed color should be stable to maintain its tint without suffering from fading,
(c) not to hinder the color developing and to provide a high rate of color development, and
(d) to produce clear and dense images without runs.
For the purpose to produce ethylbenzene, ethyltoluene and cumene, it has been widely put into industrial practice that hydrocarbons such as benzene and toluene are alkylated with olefins such as ethylene and propylene in the presence of alkylation catalysts to obtain alkylbenzenes. In this process, various kinds of alkylation catalysts such as aluminum chloride, solid phosphoric acid and boron fluoride are employed.
In the above alkylation process, heavier by-products containing diarylalkanes, triaryldialkanes and other impurities according to to the kinds of starting materials and alkylation catalyst, are obtained. As disclosed, for example, in Japanese Laid-Open Patent Publication Nos. 55-71589 and 56-161195, it is known that the heavier products, i.e ethylbenzene heavy end that is obtained from a process to alkylate benzene with ethylene in the presence of aluminum chloride catalyst, can be used as a solvent for the dye of pressure-sensitive recording paper.
The ethylbenzene heavy end disclosed in the above references are, however, not satisfactory because it contains unsaturated compounds and carbonyl compounds that cannot be easily removed only by distillation as disclosed in the above references, and accordingly, it has offensive odor and the stability of developed color is not good.
As the measure to solve these problems, the references propose the refining of the heavy end under severe conditions and the mixing of vegetable oils as masking agents. Furthermore, the solvent disclosed in the above references cannot be said that it is desirable in view of the color developing rate and the density of developed color due to chemical structures of its components of the solvent. Since the odor has naturally close relation to the chemical structures of compounds, the odors of the solvents disclosed in the above references are attributable to the components themselves as well as their impurities.